The present invention relates to stabilizing the gain (voltage to frequency) of a voltage controlled oscillator (VCO) against temperature changes so as to maintain stable deviation, in particular for use in a SECAM modulator.
The gain of most prior art VCOs varies with temperature. In an application such as a SECAM modulator, this variation is undesirable since then the deviation of the VCO having a SECAM modulating signal of given amplitude will in turn vary. This problem is especially acute in ENG (electronic news gathering) cameras, which cameras must be able to operate in environments having temperature ranges in excess of -20.degree. C. to +40.degree. C.
A gain control loop for SECAM encoders is shown in U.S. Pat. No. 4,264,918. The circuit shown therein works very accurately and is well suited for sophisticated studio applications. However, it may have a high component count and may require considerable space and power, which may render it unsuitable for ENG cameras.
It is therefore desirable to provide a VCO that has stable gain and low power and component requirements.